What is the key difference between Ethernet II framing and 802.3 framing, and why does it matter for protocol type?

• A. 802.3 uses an LLC header and a Length field, whereas Ethernet II uses a Type field to indicate the upper-layer protocol.
• B. Ethernet II uses a Type field indicating the upper-layer protocol; 802.3 uses a Length field and often an LLC header, affecting how payload is interpreted.
• C. 802.3 frames are always shorter than Ethernet II frames.
• D. Ethernet II frames rely on an LLC header for protocol identification.

Answer: (B)

How the next-layer protocol is identified in Ethernet frames differs between Ethernet II and 802.3. In Ethernet II, the 16-bit field that follows the source MAC is EtherType, indicating the upper-layer protocol directly (for example, 0x0800 for IPv4, 0x86DD for IPv6, 0x0806 for ARP). That single field tells the receiver exactly how to interpret the payload. In 802.3 framing, that position is used for the payload length, not a protocol tag. To determine the next protocol, most 802.3 frames include an LLC header (IEEE 802.2) and often a SNAP header, where the protocol is identified. Because the protocol type isn’t carried directly in the main header, devices must parse the LLC/SNAP to route the payload to the correct upper-layer protocol. This distinction matters for how frames are multiplexed and interpreted across devices and software that rely on different mechanisms to identify the next protocol.